1. Field of the Invention
This invention relates to a meter cover and meter base assembly for an electric meter and particularly to a plastic mating ring for mounting the meter cover onto the meter base. The invention is particularly suitable for an electric induction watthour meter.
2. Description of the Prior Art
For many years, a stainless steel ring has been used to attach the molded glass cover to the base of a single phase watthour meter. The circular flanged ring is assembled to the cover by welding clips onto the ring. During the welding process, the cover which is part of the assembly, is proned to breakage due to the forces applied to the metal parts to keep them on location and heat generated during welding. Large variations in the dimensions of the molded cover also aggravate the assembly process causing non-uniform loading to be applied to the glass. Metal rings, being made from thin coil stock, have sharp edges which can cause injury to a person when assembling the cover onto the base or the insertion of the complete meter into the socket. Upon installation of the meter in the field, the installer takes the meter and inserts it into a socket and then places a "U-shaped` sealing ring around the perimeter of the cover flange, ring and base. To make sure that the sealing ring fits over the assembly, the diameter and height build up the meter, ring and base are dimensioned to meet specific ANSI-limits. The sealing ring also has ANSI values limiting its size. Any change in the design of the ring, cover or base may adversely impact the fit of the sealing ring over the assembly.
It has heretofore been proposed to replace the metal rings with a plastic mating ring for mounting a meter cover to a meter base. An example of such plastic mating ring is disclosed in U.S. Pat. No. 5,499,159. While such plastic rings have been successful, nevertheless they have left something to be desired. When a plastic ring is used, it must be of sufficient strength so that it cannot be broken or be too flexible so that it can be pulled off the cover when the meter is being removed from the socket. The design of the plastic ring must be adequate to compensate for the variation in the thickness build up of the cover, base and gasket to provide both sealing of the gasket and limit the torque required to turn the ring-cover assembly onto the base. Additionally, the dimensional build up from the top of the ring to the bottom of the base should not exceed ANSI limits and the diameter of the ring cannot exceed ANSI limits.